Mutual funds are great way to diversify your investments (e.g compared to individual stocks). I am investing a significant part of my savings in a mutual fund, and understand that investment has risks (e.g. the stock market might go down like crazy). However, is it safe from the risk of default (e.g. the funds manager just not giving you your money when you try to redeem)? In the US, are there regulations that make this very unlikely to happen? Or should I try to "diversify" again by investing with multiple funds manager?
The only way for a mutual fund to default is if it inflated the NAV. I.e.: it reports that its investments worth more than they really are. Then, in case of a run on the fund, it may end up defaulting since it won't have the money to redeem shares at the NAV it published.
When does it happen? When the fund is mismanaged or is a scam. This happened, for example, to the fund Madoff was managing. This is generally a sign of a Ponzi scheme or embezzlement.
How can you ensure the funds you invest in are not affected by this? You'll have to read the fund reports, check the independent auditors' reports and check for clues. Generally, this is the job of the SEC - that's what they do as regulators. But for smaller funds, and private (i.e.: not public) investment companies, SEC may not be posing too much regulations.
There are very strict regulations that requires the assets which a fund buys on behalf of its investors to be kept completely separate from the fund's own assets (which it uses to pay its expenses), except for the published fees. Funds are typically audited regularly to ensure this is the case.
So the only way in which a default of the fund could cause a loss of invstor money would be if the fund managers broke the regulations and committed various crimes. I've never heard of this actually happening to a normal mutual fund.
There is of course also a default risk when a fund buys bonds or other non-equity securities, and this may sometimes be non-obvious. For example, some ETFs which are nominally based on a stock index don't actually buy stocks; instead they buy or sell options on those stocks, which involves a counterparty risk. The ETF may or may not have rules that limit the exposure to any one counterparty.
There is a measure of protection for investors. It is not the level of protection provided by FDIC or NCUA but it does exist:
Securities Investor Protection Corporation
SIPC protects against the loss of cash and securities – such as stocks and bonds – held by a customer at a financially-troubled SIPC-member brokerage firm. The limit of SIPC protection is $500,000, which includes a $250,000 limit for cash. Most customers of failed brokerage firms when assets are missing from customer accounts are protected. There is no requirement that a customer reside in or be a citizen of the United States. A non-U.S. citizen with an account at a brokerage firm that is a member of SIPC is treated the same as a resident or citizen of the United States with an account at a brokerage firm that is a member of SIPC.
SIPC protection is limited. SIPC only protects the custody function of the broker dealer, which means that SIPC works to restore to customers their securities and cash that are in their accounts when the brokerage firm liquidation begins.
SIPC does not protect against the decline in value of your securities. SIPC does not protect individuals who are sold worthless stocks and other securities. SIPC does not protect claims against a broker for bad investment advice, or for recommending inappropriate investments.
It is important to recognize that SIPC protection is not the same as protection for your cash at a Federal Deposit Insurance Corporation (FDIC) insured banking institution because SIPC does not protect the value of any security.
Investments in the stock market are subject to fluctuations in market value. SIPC was not created to protect these risks. That is why SIPC does not bail out investors when the value of their stocks, bonds and other investment falls for any reason. Instead, in a liquidation, SIPC replaces the missing stocks and other securities when it is possible to do so.